1. Field of the Invention
This invention relates to a system for producing purified water from feed water and for controlling its end use pressure.
2. Description of the Prior Art
Water purification systems have found increasing use in the home and the work place to raise the quality of tap water for drinking, cooking, ice making and the like. "Reverse osmosis processes" are a known class of processes in general use in these systems. These processes employ "reverse osmosis membranes" which are selectively impermeable to dissolved salts in aqueous solution. Some typical prior art purification systems include, in addition to the reverse osmosis membrane permeator, a pre-filter for initial screening of the feed water to prevent clogging and to protect the membrane, and a post-filter for further purification, especially for the removal of organics such as dissolved hydrocarbons. In general, in these systems, tap water or feed water is filtered and separated as product water and waste water.
Reverse osmosis membrane permeators constitute a major restriction to the flow of water through these purification systems, and so the filtration process is relatively slow. Therefore, a system of a size which is economically and aesthetically practical for the home is generally not able to generate product water on demand but must include a product water storage reservoir. Pressures within the system require control to optimize the system operation. Finally, waste water must be disposed of.
The prior art includes U.S. Pat. Nos. 4,021,343, 4,176,063, 4,391,712 and 4,695,375 to Tyler and 4,604,194 to Entingh. Tyler Pat. No. 4,021,343 describes an automatic purifier system including a reverse osmosis filter having an inlet for connection to a source of feed water, and a product water outlet leading to a reservoir having a pressure bladder. Waste water from the filter provides motive pressure on the opposite side of the bladder. A number of pilot and control valves are used to control the product and waster water flows.
Tyler Pat. No. 4,176,063 describes an improvement and simplification of the earlier Tyler Pat. No. 4,021,343. Among other things, it adds the capability of delivering water to an ice maker. In this later Tyler system, feed water flows through an inlet valve to a filtration unit. Product water flows from the filtration unit to a reservoir and to a pilot control for the inlet valve. Waste water flows from the filtration unit to a pressure control valve and from there to the pressure side of the bladder in the reservoir. The pressure control valve is controlled by pilot pressure of the product water.
Entingh Pat. No. 4,604,194 describes a water purification system including shut-off valve, regulating valve, reverse osmosis membrane, and bladder-pressurized reservoir. The regulating valve operates in response to product water pressure.
Additional prior art, relevant only to components of this system, includes U.S. Pat. Nos. 3,493,496 to Bray et al; 3,794,173 to Bray; and 3,789,993; 3,792,135; and 3,824,299 to Brown et al. Bray et al Pat. No. 3,493,496 discloses a water purification system having a bladder or diaphragm which is pressurized by water or air to provide motive pressure to the product water. Bray Pat. No. 3,794,173 discloses a water purification system with a hydraulically actuated valve, controlled by product water pressure, to raise motive pressure when water is withdrawn. Brown et al Pat. Nos. 3,789,993; 3,792,135; and 3,824,299 disclose the specifics of composition and manufacture of reverse osmosis membrane permeators which are used in this invention.